Transparent conductive films are very important for many electronic devices and components. They are mostly used for electrode applications in devices such as liquid crystals, flat panels or plasma displays, touch panels, organic light emitting diodes (OLED) and solar cells. Such films especially are used for thin film cells, organic polymer cells (OPC) and dye-sensitized solar cells.
Transparent conductive film materials are usually made from doped metal oxides, most commonly indium tin oxide (ITO). However ITO has a number of drawbacks and is unlikely to be the material of choice in future optoelectronic devices.
The problems with ITO films and layers revolve around the cost of indium, its material performance and process conditions used in their production. The latter two issues become more significant, due to the increase of display sizes in the future and the use of flexible plastic film materials instead of glass. The new types of displays have to be very flexible and have to include transparent electrodes which can be produced at low temperature and low costs, and if desired have to be of very large size. In top these display have to have a low sheet resistance and high transparency.
It is straightforward to achieve sheet resistance of about 10 Ohm/sq for transmittance of >90% with ITO.
Alternative materials are under investigation since several years. In order to catch the ITO level, new nanostructure thin film materials are in focus of new TC (transparent conductive) materials. Graphene and carbon nano tube films have been studied. However, the main issue is still the sheet resistance and high transparency.
Another group of new nanostructure thin film materials are silver nanowires films (AgNW). Latest results did show very promising results in comparison with ITO standard. It was possible to achieve a sheet resistance of about 13 Ohm/sq for transmittance of 85%. Therefore, it is expected a wide implementation of the AgNW technology for display and photovoltaic market in future due to a simplified production of these nanomaterials and a low cost deposition method on plastic-film or glass substrates. (Sukanta, D.; Thomas, M. H.; Philip, E. L.; Evelyn, M. D.; Peter, N. N.; Werner, J. B.; John, J. B.; Jonathan, N. C., (2009). “Silver Nanowire Networks as Flexible, Transparent, Conducting Films: Extremely High DC to Optical Conductivity Ratios”. American Chemical Society.
The solar power market has continuously grown and the ability to create high-efficiency solar cells is a key strategy to meet the growing world energy needs. Today's photovoltaic systems are predominantly based on the use of crystalline silicon, thin-film and concentrator photovoltaic technologies.
Thin-film technologies have lower efficiencies than crystalline silicon cells but permit the direct deposition to a surface that can be made of a flexible polymer material or plastic. Thin-film technology reduces the costs of the end product because it allows to use smaller amounts of semiconductor material, while the manufacturing is done in a continuous process, and it results in a product that is less likely to be damaged during transportation.
Thus, a promising low cost alternative product in comparison to silicon solar cells or semiconductor devices can be found in organic photovoltaic devices (OPVs) as well, if their power conversion efficiency can be increased (Liquing, Y.; Tim, Z.; Huaxing, Z.; Samuel, C. P.; Benjamin J. W.; Wei, Y., (2011). “Solution-Processed Flexible Polymer Solar Cell with Silver Nanowire Electrodes”. Curriculum of Applied Sciences and Engineering.
Organic (polymer-based) solar cells are flexible, and according to the current state of development, their production costs are about a third of the price of silicon cells. They are disposable and can be designed on a molecular level. Current research is focusing on the improvement in efficiency and on the development of high-quality protective coatings in order to minimize the environmental effects.
According to the current state of the art, in a Silver-Nanowire-, or Carbon-Nanotube-, or a polymer based substrate any desired structure can be etched selectively and directly by laser-supported etching methods or, after masking, by wet-chemical methods or by dry-etching methods.
In laser supported etching methods the laser beam scans the entire etch pattern dot by dot or line by line in the case of vector-orienting systems, on the substrate, which, in addition to a high degree of precision, also requires considerable adjustment effort and is very time-consuming.